1. Field of the Invention
The present invention relates to direct fired boilers used to supply heated water for a large building. In particular, the invention relates to a method and apparatus for saving energy in the operation of a large building employing one or more direct fired boilers.
2. Description of the Related Art
Direct fired boilers are well known in the art and are commonly employed in large buildings to provide heated water for use at various locations in the building. Water is heated in direct fired boilers by burning natural gas or other fuel. The water may also be heated by electrical heating coils, if desired.
Water heated in direct fired boilers is pumped to the various locations throughout the building requiring heated water. Some direct fired boilers are used to provide heated water for lavatory and shower facilities located in the building, and for kitchens and cooking facilities in the building requiring hot water for washing dishes and other utensils. Such hot water uses require that the hot water be removed from the hot water lines extending from the direct fired boilers and therefore fresh water must be continually added to the direct fired boilers to replace the water withdrawn. The heated water supplied to such locations is referred to herein as domestic hot water.
Other direct fired boilers are used for supplying heated water to heating coils located throughout the building. The heating coils are used for heating the air within the building. After heated water is circulated through the heating coils, it is returned to the boiler for reheating. Such heating coils are commonly located in the ducts or vents sometimes referred to in the art as air handlers supplying air to the various rooms in the buildings to heat the air flowing into the rooms when desired. Heated water supplied to such heating coils from direct fired boilers is referred to herein as reheat water.
Direct fired boilers supplying reheat water are boilers which maintain the water heated therein at a temperature below the boiling point of water and do not produce steam. The temperature of the water in a direct fired boiler is commonly controlled by a conventional thermostat.
Reheat water is used to heat air in the building at various locations throughout the building. The heating coils receiving reheat water are commonly located adjacent to cooling coils receiving chilled liquids or gases from air conditioning units. Both the cooling coils and the heating coils are commonly located adjacent to each other in the duct or air handler supplying conditioned air to a room in a building. If it is desired to raise the temperature of a room being cooled by air blown over cooling coils, reheat water is directed to heating coils which are located in the airstream blown over the cooling coils. Thus the heating coils receiving reheat water can raise the temperature of the conditioned air being introduced into a room as desired.
Domestic hot water should not be mixed with reheat water because the reheat water usually contains chemicals or other additives to prevent scaling or contamination of reheat water flowlines that would contaminate domestic water. Therefore, separate direct fired boilers are required to furnish domestic hot water and to furnish reheat water.
It is common in large buildings for multiple direct fired boilers to be utilized to furnish reheat water. Multiple direct fired boilers are desired for many reasons. One of the reasons is that if one of the boilers cannot be used due to mechanical failure or routine maintenance, the other boiler or boilers may be utilized. Furthermore, it is sometimes necessary to utilize all or most of the boilers in order to adequately heat the building and supply reheat water to various locations in the building.
Direct fired boilers are commonly connected in parallel. Parallel connected direct fired boilers supply reheat water to a common manifold or header and receive reheat water returned from heating coils through a common manifold or header.
Furthermore, it is quite common for all direct fired boilers supplying reheat water to be operated continuously, twenty-four hours a day, even though the heating capacity of all boilers is not required to supply the reheat water needed by the building.